Standard image sensors have a limited dynamic range of about 60 to 70 dB or less. For example, an 8-bit sensor has a dynamic range of only 48 dB. However, the luminance dynamic range of the real world is much larger and natural scenes often span a range of 90 dB or more. When an image sensor captures a scene with a luminance dynamic range in excess of the sensor dynamic range, information is necessarily lost. Depending on the exposure settings, the brighter regions may be saturated and/or the dimmer regions may be underexposed, producing a captured image of a quality unable to reproduce the actual scene.
In order to simultaneously capture highlights and shadows of a scene, image sensors have used High Dynamic Range (HDR) technologies to increase the captured dynamic range. One of the most common techniques to increase the dynamic range is to merge multiple exposures, captured with a standard, low dynamic range image sensor, into a single HDR image that has a much larger dynamic range than a single exposure image. For instance, images of the same scene could be recorded at a series of different exposure times, where the longest exposure is set to optimally capture the dimmest portions of the scene and the shortest exposure is set to optimally capture the brightest portions of the scene. However, such image combination methods frequently suffer from artifacts caused, for example, by objects in the scene moving between exposures.
HDR color image sensors that capture an HDR color image in a single frame have been developed. One example hereof is an image sensor where every other row of the color pixel array operates at a shorter exposure time. Bright light data and low light data are obtained from the rows operating at the shorter exposure time and longer exposure times, respectively. Another example is an image sensor based on pixels that are characterized by a piecewise linear photoresponse curve. The photoresponse curve is composed of linear segments of different photoresponsivity. During exposure, the pixels are partially reset multiple times to acquire data corresponding to these different photoresponsivities. However, both of these sensors may still suffer artifacts associated with moving objects, as the time periods for acquiring data from different portions of the dynamic range are not identical.